Much of the javascript and css now comes from the bedrock repository:
If you look in Concrete’s webpack.mix.js file, you’ll see the files that get pulled in from bedrock and processed, so for frontend.js
So this is where it’s pulling that from:
Some of the things that might get pulled in are going to be third-party libraries, that won’t exist as such in the repo, they’ll be dependancies that get pull in when you run an npm build.